Advanced Materials Research Vols. 1120-1121

Abstract: The hot deformation behavior of nanoprecipitation strengthening steel was studied using a Gleeble-3500 thermo-mechanical simulator. The results show that the peak stress reduces as the temperature increases, and increases as the strain rate increases. The dynamic recrystallization will more likely occur at higher deformation temperature and lower strain rate. The deformation activation energy of the tested steel at 950-1150^οC is calculated to be 333.844kJ/mol by regression analysis. Flow stress equation of the tested steel is also established.

Abstract: When submitted to annealing thermal treatments Shape Memory Alloys have their phase transformation temperatures effected. The aim of the present work is to investigate the effects of cooling time in the phase transformation temperatures of Ni₅₅Ti₄₅ in w.t. % alloy annealed at 350°C. Samples of this alloy were maintained at 350°C for one hour and then cooled in the same furnace for 10 minutes, 1 hour and 24 hours. The phase transformation temperatures were measured by means of Differential Scanning Calorimetry (DSC) at cooling and heating rates of 20°C/min. The results show that the annealing at 350°C changed the phase transformation up to 54%. For 10 minutes cooling time the M_f temperature increase from 15,65°C to 24,1°C. For the others cooling times the phase transformation temperature did not change significantly. Therefore, the cooling time for the annealing at 350°C did not effect the phase transformation temperatures of the Ni₄₅Ti₅₅ in wt % shape memory alloy.

Abstract: The constant magnetic field effect (B≤0.6 T) on creep of polycrystalline copper and its dislocation substructure has been established. The correlation of creep rate to time up to failure has been determined. The magnetic field effect on change of dislocation substructure parameters depending on the distance to the surface of failure (at a distance of 2, 4, 7, 10 and 20 mm from the surface of failure) under creep has been studied. It has been shown that magnetic field affects greatly the redistribution of dislocation substructure types and their scalar density of dislocations. The magnetic field effect on polycrystalline copper is connected with magneto-induction relaxation of dislocation structure.

Abstract: The bond strength were comparatively measured by tensile test, tension shear test and compression shear test in order to evaluate bonding behavior of thin aluminum clad steel strips bonded by cold rolling, and furthermore determine minimum stable reduction of clad strips. The morphologies after fracture were observed and analyzed using SEM (scanning electron microscope) and EDS (energy dispersive spectrometer). The results show that it is lower for the bond strength obtained by shear test than one obtained by tensile test, which largely attributes to different stress states during testing. Minimum stable reduction can be defined as one beyond which the fracture would completely occur at aluminum component layer instead of interface between components, which is suggested as 40-45% based on fracture feature of Al clad steel strip.

Abstract: In this study, the wear behavior of AM60 alloys adding different amounts of yttrium (0, 0.5, 1, 1.5, and 2 wt%) during dry sliding has been investigated. The microstructure observation and EDS analysis demonstrated that adding yttrium in AM60 alloy formed a new phase Al₂Y and minimized the precipitation of Mg₁₇Al₁₂ phase. The wear rate and friction coefficient of AM60 alloys adding yttrium were lower than that AM60 alloy under the same condition. The worn surface was covered with long continuous grooves parallel to the sliding direction. The wear resistance of AM60 alloy was improved when yttrium was added due to the formation of uniformly is tribute finer and harder Al₂Y precipitates. The harder Al₂Y precipitates increased the hardness and wear resistance of the AM60 alloy and reached the maximum at 1 wt% Y.

Abstract: Using optical microscopy、impact and tensile test,Study the effects of different quenching and tempering temperature on the microstructure and mechanical properties of the steel 20SiMn2MoVA.The results showed that, at the test temperature range,with the rise of quenching temperature the tensile strength of steel 20SiMn2MoVA declining, Low-temperature impact energy along with the quenching temperature rise was increasing. After quenching at 920°Cand tempering at different temperatures, with increasing tempering temperature, the tensile strength of the material showed a declining trend, impact toughness values were rising trend has decreased, 220°Ctempered impact toughness appear peak. Below 300°C tempering is tempered martensite and a small amount of residual austenite; More than 300°C tempering, residual austenite begins to decompose, carbide separeated out, 400°Ctempering is tempered flexor s body. Test material at 920°Cafter quenching and tempering 220°C, has good strength and toughness, specific properties: tensile strength 1506 MPa and temperature impact toughness A_kv 35.6J.

Abstract: In this study, the hexachloroethane (C₂Cl₆) as a refiner was introduced into a cylindrical squeeze casting of magnesium alloy AM60 with a diameter of 100 mm and a thickness of 25 mm. The casting was prepared under an applied pressure of 30 MPa. The results of tensile testing indicate the tensile properties for the C₂Cl₆-refined specimens were significantly improved over the untreated AM60 samples. Microstructure analyses with optical microscopes reveal the great grain refining capability of C₂Cl₆ on squeeze cast magnesium alloy AM60, which should be responsible for the enhanced tensile properties of the refined AM60.

Abstract: The quenching process of 20 steel and 45steel is investigated in the paper and the changing law of martensite in carbon steel is discussed. The carbon content in 20steel and 45steel is both less than 0.77%,which means they are hypoeutectoid steel. The microstructure of 20 steel after quench shows lath shape while martensite in that of 45steel exhibits both lath shape and flake which occupies approximately 80%. The plasticity and toughness of martensite depend on the substructure, that is, the toughness of dislocation martensite is better than that of twin martensite under the same condition.

Abstract: Bimetallic castings are widely employed as working elements in winning machines which work in conditions of intensive friction wear. The main features of wear are: dynamic percussive loads, intensive abrasive wear caused by erosion and corrosion. Three cylindrical rods cavities of the same dimensions of φ 20x200 mm were made in sand mould. Different amount of liquid iron alloy with carbon equivalent of 4.14, Mn of 0.58 and Cu of 0.17 wt% was poured into the three rod cylindrical cavities over the solid 304 stainless steels cylindrical desks inserts. Good coherent interfaces for all liquid/Solid volumes (16 to 24) are produced and multi-layers interfacial microstructure bimetal are produced. Increasing the liquid/solid volumes from 16 to 24 increases the thickness of transient layer from 52 to 89 μm and decreases the amount of ledeburite in the structure of solidified gray cast iron.

Abstract: The influence of inclusion on pitting corrosion of X80 pipeline steel was investigated by using electrochemical test and atomic force microscope. The results indicated that corrosion potential of X80 pipeline steel sample with higher grade inclusion was lower, and decreased significantly with chloride ion concentration increasing. Inclusion was not conducive to corrosion resistance of X80 pipeline steel. The way of X80 pipeline steel pitting corrosion was that pit formed at the inclusion dissolution, and grew to pitting. There were less corrosion products near the pit hole, forming a cathode ring.